Amino Amide vs Amino Ester Local Anesthetics: Types and Metabolism

Local anesthetics can be broadly classified into two groups based on their molecular structure and metabolic pathways:

Amino Amides

These local anesthetics are primarily metabolized in the liver and are known for their stability in solution. Common examples include lidocaine, bupivacaine, and ropivacaine. They are generally used in procedures where a longer duration of action is beneficial and are less likely to cause allergic reactions. Commonly used amide local anesthetics include lidocaine, bupivacaine, ropivacaine, and mepivacaine, with levobupivacaine also being popular outside of the United States.  Amides can, in most cases, be identified by having two “i’s” in their name.

Amino Esters

Metabolized quickly by plasma esterases, these agents are less stable in solution and have a shorter duration of action. They include agents like procaine and tetracaine. Esters are more likely to cause allergic reactions due to their metabolites, which can complicate their use in patients with specific sensitivities.  Commonly used ester LAs include chloroprocaine, procaine, and tetracaine.

Practical Considerations

When choosing a local anesthetic, several factors must be considered, including the desired duration of anesthesia, the potential for systemic toxicity, and the patient's history of allergies. The physical and chemical properties of the anesthetic, such as lipid solubility and protein binding capacity, influence its onset and duration of action and can affect its overall efficacy and safety profile.